Changes

requirements: set cmd2>=2.6.2,<3.0

Remove the previous workaround that set cmd2==2.4.3 in jenkins.sh. The
bug this worked around has been fixed in 2.6.2.

3.0 will break unless we use some new additional decorator.

Related: OS#6776
Change-Id: I4ba65ed486247c5670313b75f43a242d264df14b